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D A Kendall

Publications and source records attributed to D A Kendall.

At least 163 records · Page 9Linked to original sources
PubMed1984

Inositol phospholipid hydrolysis in rat cerebral cortical slices: I. Receptor characterisation.

Characterisation of receptor-mediated breakdown of inositol phospholipids in rat cortical slices has been performed using a direct assay which involves prelabelling with [3H]inositol. When slices were preincubated with [3H]inositol, lithium was found to greatly amplify the capacity of receptor agonists such as carbachol, noradrenaline, and 5-hydroxytryptamine to increase the amount of radioactivity appearing in the inositol phosphates. Using a large variety of agonists and antagonists it could be shown that cholinergic muscarinic, alpha 1-adrenoceptor, and histamine H1 receptors appear to be linked to inositol phospholipid breakdown in cortex. The large responses produced by receptor agonists allowed a clear discrimination between full and partial agonists as well as quantitative analysis of competitive antagonists for each receptor. Whereas carbachol and acetylcholine (in the presence of a cholinesterase inhibitor) were full agonists, oxotremorine and arecoline were only partial agonists. Very low concentrations of atropine shifted the carbachol dose-response curve to the right and allowed inhibition constants for the antagonist to be easily calculated. The nicotinic antagonist, mecamylamine, was ineffective. Noradrenaline adrenaline were full agonists at alpha 1-adrenoceptors, but phenylephrine and probably methoxamine were partial agonists. Prazosin, but not yohimbine, potently and competitively antagonised the noradrenaline inositol phospholipid response. Mepyramine but not cimetidine competitively antagonised the histamine response. These data provide strong confirmation for the potentiating effect of lithium on neurotransmitter inositol phospholipid breakdown and emphasise the ease with which functional responses at a number of cortical receptors can be characterised.

Animals↗
PubMed1984

Inositol phospholipid hydrolysis in rat cerebral cortical slices: II. Calcium requirement.

The calcium requirement for agonist-dependent breakdown of phosphatidylinositol and polyphosphoinositides has been examined in rat cerebral cortex. The omission of added Ca2+ from the incubation medium abolished [3H]inositol phosphate accumulation from prelabelled phospholipid induced by histamine, reduced that due to noradrenaline and 5-hydroxytryptamine, but did not affect carbachol-stimulated breakdown. EC50 values for agonists were unaltered in the absence of Ca2+. Removal of Ca2+ by preincubation with EGTA (0.5 mM) abolished all responses, but complete restoration was achieved by replacement of Ca2+. The EC50 for Ca2+ for histamine-stimulated [3H]inositol phosphate accumulation was 80 microM. Noradrenaline-stimulated breakdown was antagonised by manganese (IC50 1.7 mM), but not by the calcium channel blockers nitrendipine or nimodipine (30 microM). The calcium ionophore A23187 stimulated phosphatidylinositol/polyphosphoinositide hydrolysis with an EC50 of 2 microM, and this response was blocked by EGTA. Omission of Ca2+ or preincubation with EGTA or Mn2+ (EC50 = 230 microM) greatly enhanced the incorporation of [3H]inositol into phospholipids. The IC50 for Ca2+ in inhibiting incorporation was 25 microM. The results show that different receptors mediating phosphatidylinositol/polyphosphoinositide breakdown in rat cortex have quantitatively different Ca2+ requirements, and it is suggested that rigid opinions regarding phosphatidylinositol/polyphosphoinositide breakdown as either cause or effect of calcium mobilisation in rat cortex are inappropriate.

Animals↗
PubMed1984

Effect of adrenocorticotropin administration on beta-adrenergic receptor adaptations in rat brain cerebral cortex.

It has been reported that adrenocorticotropin (ACTH) administration reduces the time necessary for observing the imipramine-induced decline in beta-adrenergic receptor binding and function in rat brain frontal cortex. This interaction was examined in the present study following the destruction of the dorsal noradrenergic bundle in an attempt to determine whether the hormone treatment influences pre- or postsynaptic activity to facilitate the receptor response. Lesioning completely prevented the decline in beta-receptor binding normally observed following treatment with the drug combination. In fact, the number of cerebral cortical beta-adrenergic receptor binding sites was significantly greater in lesioned animals receiving ACTH than in lesioned controls. Lesioning significantly increased the amount of cyclic AMP produced in response to a saturating concentration of norepinephrine, an effect that was not influenced by ACTH treatment. These findings suggest that ACTH administration modifies the norepinephrine-stimulated cyclic nucleotide system indirectly, perhaps through an action on presynaptic neurons, whereas the effect on receptor recognition site number may be due to a direct action on the postsynaptic cell.

Adrenocorticotropic Hormone↗
PubMed1983

Characterization of a fluorescence assay to monitor changes in the aqueous volume of lipid vesicles.

The fluorescent compound, 4',5'-bis[N,N-bis(carboxymethyl)aminomethyl] fluorescein (calcein) has been characterized for use in lipid vesicle studies. Particularly useful is its reaction with Co2+, which results in fluorescence quenching. This is accompanied by about a 10-nm blue shift in the uv absorbance bands and a small reduction in the visible absorbance band. For vesicle studies, Co2+ may be combined with citrate, which does not significantly hinder calcein quenching by Co2+. It does augment the absorbance of the metal ion. No significant interaction of citrate X Co2+ with phosphatidylserine vesicles was observed. Zn2+ is capable of displacing Co2+ and restoring calcein fluorescence. Fluorescence quenching due to formation of the calcein X Co2+ complex can also be reversed with EDTA. Thus, calcein is the basis of some simple reactions which can be used to assay changes in the aqueous volume of lipid vesicles.

Buffers↗
PubMed1983

Detergent effects on enzyme activity and solubilization of lipid bilayer membranes.

Over 50 detergents were tested to establish which would be most effective in releasing proteins from membrane-bounded compartments without denaturing them. Various concentrations each of detergent were tested for two activities: (1) solubilization of egg phospholipid liposomes as measured by reduction of turbidity and (2) effect of detergent concentration on the activities of soluble, hydrolytic enzymes. Those detergents most effective in solubilizing 0.2% lipid and least detrimental to enzymes were five pure, synthetic compounds recently introduced: CHAPS, CHAPSO, Zwittergents 310 and 312, and octylglucoside. Industrial detergents were generally much inferior, insofar as they solubilized membranes inefficiently and/or inactivated certain hydrolytic enzymes readily. The five detergents were characterized by (a) an unusually high critical micelle concentration and (b) a preference for forming mixed micelles with lipids instead of forming pure micelles, as indicated by an ability to solubilize lipid at concentrations of detergent significantly below the critical micelle concentration. This characteristic permits solubilization of high concentrations of membrane below the critical micelle concentration of the detergent so that protein denaturation is minimized. A generally applicable guideline that emerged from this study is that detergents should be used at approximately their critical micelle concentration which should not be exceeded by the concentration of membrane. Similar considerations should apply to the use of detergents in purifying and reconstituting intrinsic membrane proteins.

Alkaline Phosphatase↗
PubMed1983

THIP analgesia: cross tolerance with morphine.

THIP (4,5,6,7-tetrahydroisoxazolo (5,4-c) pyridone-3-ol), a direct acting GABA receptor agonist, has been shown to have antinociceptive properties. To determine whether tolerance develops to the analgesic response, mice received multiple injections of THIP for up to 21 days after which analgesia was tested using both tail immersion and hot-plate methods. Both tests indicated a significant reduction in the antinociceptive response to THIP, as well as other GABA agonists, beginning between days 3 and 5 of chronic administration. Moreover, these animals demonstrated a decreased analgesic response to morphine, and morphine tolerant animals were also less responsive to THIP. These data indicate that opiates and GABA agonists induce analgesia by acting through separate but related pathways in the central nervous system.

Analgesia↗
PubMed1983

Sendai virus-mediated lysis of liposomes requires cholesterol.

Vesicles were constituted with glycophorin, the Sendai virus receptor of human erythrocytes, and loaded with calcein, a polar derivative of fluorescein, at self-quenching concentrations. On exposure to Sendai virus and mild hypo-osmotic stress, vesicles of the appropriate composition released a significant portion of their internal contents, as indicated by an increase in calcein fluorescence. Susceptible liposomes were not induced to leak by heat-inactivated virus or by trypsin-treated virus. The response of the vesicles to virus attachment is thus analogous to virus-induced hemolysis and presumably involves fusion of the vesicle and virus membranes. In addition to glycophorin and phosphatidylcholine, cholesterol was absolutely required for the lytic response to the virus. The need for cholesterol was not attributable to inactivation of the virus by liposomes without cholesterol. The presence of gangliosides increased the encapsulated volume of the liposomes, but gangliosides did not effectively substitute for glycophorin. Thin-layer chromatography of lipid extracted from incubated virus and liposomes containing a small amount of a fluorescent phosphatidylcholine indicated that phosphatidylcholine in the vesicle is not chemically altered by functional interaction with the virus.

Cell Aggregation↗
PubMed1983

Temperature-dependent 5-hydroxytryptamine (5-HT)-sensitive [3H]spiperone binding to rat cortical membranes: regulation by guanine nucleotide and antidepressant treatment.

5-Hydroxytryptamine (5-HT)-sensitive binding of [3H]spiperone to rat cortical membranes was examined at 22 degrees C and 37 degrees C. At the lower temperature a significantly higher density of specific sites with identical affinity for [3H]spiperone (0.15 nM) was observed. Furthermore, a proportion of sites at 22 degrees C, although not at 37 degrees C, possessed high affinity for 5-HT and these were apparently converted to low affinity sites by GTP (100 microM). Examination of the apparent affinities of the 5-HT derivatives 5-methoxytryptamine, 5,6-dihydroxytryptamine and tryptamine revealed differences in the potencies of these analogs that were particularly evident for the high affinity proportion of sites observed at 22 degrees C. Subchronic treatment of rats with the antidepressants mianserin and iprindole reduced the density of [3H] spiperone binding sites when assays were performed at either temperature. However, antidepressant treatment appeared to preferentially reduce the number of sites that possess high affinity for 5-HT.

Animals↗
PubMed1983

[3H]tetrahydrotrazodone binding. Association with serotonin binding sites.

High (17 nM) and low (603 nM) affinity binding sites for [3H]tetrahydrotrazodone ([3H] THT), a biologically active analogue of trazodone, have been identified in rat brain membranes. The substrate specificity, concentration, and subcellular and regional distributions of these sites suggest that they may represent a component of the serotonin transmitter system. Pharmacological analysis of [3H]THT binding, coupled with brain lesion and drug treatment experiments, revealed that, unlike other antidepressants, [3H] THT does not attach to either a biogenic amine transporter or serotonin binding sites. Rather, it would appear that [3H]THT may be an antagonist ligand for the serotonin binding site. This probe may prove of value in defining the mechanism of action of trazodone and in further characterizing serotonin receptors.

Animals↗
PubMed1982

A fluorescence assay to monitor vesicle fusion and lysis.

An assay based on the fluorescent compound 2',7'-([bis(carboxymethyl)amino]methyl) fluorescein (calcein) has been developed to investigate vesicle fusion and lysis. The assay involves encapsulating the nonfluorescent Co2+ complex of calcein in one set of vesicles and EDTA in a second set. If fusion occurs, EDTA chelates Co2+, releasing calcein which may be assayed by means of its intense fluorescence. Leakage of either component of the reaction can be directly quantitated by titrating the external medium with the other component. This assay was used to investigate the effects of calcium ion on small phosphatidylserine vesicles, a system reported to undergo fusion. It revealed immediate and extensive leakage of the encapsulated contents; membrane fusion must, therefore, be simultaneously with or subsequent to, loss of vesicle integrity. This assay is convenient and flexible; it should be useful in a variety of investigations of membrane-bounded compartments.

Animals↗
PubMed1982

The influence of ACTH and corticosterone on [3H]GABA receptor binding in rat brain.

Bilateral adrenalectomy (ADX) induces a significant, regionally selective, increase in GABA, but not cholinergic muscarinic or alpha1-adrenergic, receptor binding in rat brain. The increase in GABA receptor binding in the midbrain occurs within 72 h of surgery, whereas that found in the corpus striatum becomes evident between 1 and 2 weeks later. These ADX-induced receptor changes are counteracted by the administration of corticosterone, a reversal which can occur within 24 h following a single administration of steroid. Unlike ADX, hypophysectomy causes a significant reduction in [3H]GABA receptor binding in these two brain areas, an action that is not reversed by corticosterone treatment. Furthermore, systemic administration of either ACTH1-39 or ACTH4-10 in unoperated animals causes an increase in midbrain and striatal GABA receptor binding similar to that observed in ADX animals. The increase in [3H]GABA binding observed after ACTH administration appears to be due to the appearance of low affinity, high capacity binding sites not observed in untreated animals. ADX had no effect on high affinity of GABA uptake, glutamic acid decarboxylase or GABA content in the brain regions where receptor modifications were noted. These findings indicate that GABA receptor binding in rat brain can be modified by changes in the circulating levels of ACTH.

Adrenalectomy↗
PubMed1982

Trimethyltin inhibits uptake of neurotransmitters into mouse forebrain synaptosomes.

Trimethyltin (TMT), in a concentration dependent manner, inhibits in vitro uptake of gamma-aminobutyric acid (GABA), norepinephrine and serotonin by mouse forebrain synaptosomes with IC50S of 75, 43 and 24 microM, respectively. At 2 h and 14 h following in vivo administration of TMT (4.26 mg/kg; i.p.) to mice, GABA and serotonin uptake by forebrain synaptosomes are decreased, although norepinephrine uptake was not significantly affected. In vitro kinetic analyses of TMT inhibition of forebrain synaptosomal uptake of GABA, norepinephrine and serotonin indicated that the inhibition was not of the competitive type. This inhibition of uptake of neurotransmitters could be responsible, at least in part, for altered neurotransmitter levels in the synaptic cleft and may contribute to altered nervous system function during TMT intoxication.

Animals↗
PubMed1982

The influence of sex hormones on antidepressant-induced alterations in neurotransmitter receptor binding.

Long term (21-day) treatment with antidepressants induces a decrease in beta-adrenergic and serotonin 2 (5-HT2) receptor binding in rat brain frontal cortex. Since hormone imbalances are known to be associated with affective illness, the present study was undertaken to determine whether sex hormones influence these alterations in neurotransmitter receptor binding. Using receptor binding assays, we found that castration abolishes the decline in the concentration of 5-HT2, but not beta-adrenergic, receptors brought on by chronic imipramine or iprindole treatment in both male and female rats. In contrast, the receptor responses to trazodone, mianserin, and pargyline were not influenced by surgery. Furthermore, mianserin was found to reduce beta-adrenergic binding in intact females, but not males, suggesting a sex-related specificity with regard to the response to this agent. Testosterone and estrogen, but not dihydrotestosterone, reversed the effects of castration in males, suggesting that the interaction between the steroids and antidepressants is mediated through estrogenic, rather than androgenic, receptors. The results indicate that the receptor responses to some antidepressant drugs is dependent, at least in part, on the hormonal state of the animals.

Animals↗
PubMed1982

Comparison of the antinociceptive effect of gamma-aminobutyric acid (GABA) agonists: evidence for a cholinergic involvement.

The antinociceptive action of three classes of gamma-aminobutyric acid (GABA) agonists was examined in mice using the hot-plate and tail-immersion tests. A significant increase in reaction time was noted in the hot-plate test after treatment with the direct-acting GABA receptor agonists, kojic amine or 4,5,6,7-tetrahydroisoxazolo[5,4-C] pyridin-3-ol, with gamma-vinyl GABA, an inhibitor of GABA degradation, or with nipecotic acid ethyl ester, an inhibitor of high-affinity GABA transport. Studies with naloxone indicated that the increase in pain threshold was not mediated through the brain opiate system, although it was possible to reverse the antinociceptive effect of these drugs with atropine. Receptor binding experiments indicated that except for the ethyl ester of nipecotic acid, the GABA agonists have little affinity for the cholinergic muscarinic receptor site. Atropine, at a dose that completely blocked the antinociceptive action of kojic amine, was unable to attenuate the sedative effects of this drug. These findings suggest that, regardless of their mechanism, the three types of GABA agonists tested are capable of inducing an antinociceptive response in mice and that this action is apparently secondary to a GABA-mediated increase in brain cholinergic function.

Analgesics↗
PubMed1981

Imipramine: effect of ovarian steroids on modifications in serotonin receptor binding.

Long-term administration of imipramine caused a decrease in serotonin2 receptor binding in rat brain cerebral cortex, an effect that was abolished by ovariectomy. In contrast, ovariectomy had no effect on imipramine-induced decreases in hippocampal serotonin or in cerebral cortical and hippocampal beta-adrenergic receptor binding. Administration of estradiol or progesterone separately or in combination reestablished the effect of imipramine treatment on cortical serotonin2 receptors. These results suggest that ovarian steroids may play an important, but subtle, role in the neurochemical and perhaps clinical response to this drug.

Animals↗